The interdependency of aircraft technological systems, the global reach of the aviation transport industry, and die uncertainty surrounding potential atmospheric effects have made defining the relationship between aviation and environmental impact an arduous task. Air travel continues to experience the fastest growth of all modes of transport, and although the energy intensity of the aviation transport system continues to decline, fuel use and total emissions have steadily risen. This trend, which represents a conflict between growth and environmental impact, has motivated the aircraft manufacturing and airline industries, the scientific community, and governmental bodies to consider what pace of emissions reduction is acceptable. This paper analyzes the historical influence of aircraft performance on cost to examine the potential pace of future efficiency improvements and emissions reduction. Technological and operational influences on aircraft energy intensity are quantified and correlated with direct operating cost and aircraft price using analytical and statistical models built upon historical data for US airlines. The energy intensity reduction potential and economic characteristics of future aircraft are also projected, through extrapolations of historical trends in aircraft technology and operations.